Breaker Panel vs Fusible Panel?

[ElectDesigner]

I recently spoke to a designer (designs distribution systems mostly for commercial buildings) who told me that he prefers distribution panels with fusible units when he needs to supply HVAC units, he tells me that fuses have better characteristics when dealing with mechanical units.

I have seen distribution panels with breakers ( HACR breakers) that feed hvac units.

So my question is this when designing a distribution system for say a commercial project (below 600V) when do you choose a breaker panel and when do you choose one with fuisble disconnects? what are the advantages one offers over the other? (I understand that a lot of time the HVAC unit specifies max fuse or max breaker size, but it this information is not known beforehand what is a good way of going about it)

 

[templdl]

Unless HVAC manufacturer recommends fuse I personally would stay with breakers. Have you ever had a fuse blow and now it's a search for that spare fuse that you put somewhere, where you wouldn't loose it. And those fuses aren't a dollar each either. You don't want to keep too many spares because they can be expensive. And then you used that spare the other day and forget to replace it.
Then there is the why did the fuse blow in the first place? You stick another in and it's $$. Did it get taken out because it was overloaded of wiped out because of a fault?
And then have you ever tested a fuse see if will function correctly or after it blew to see if it was within specification? Of do just trust that they are manufactured to the correct specifications.

AHHHHHHHH, then there is the breaker, if the breaker tripped on overload and you are there when it tripped, it normally will take a short time before the thermal element to cool off a bit before the breaker will latch. If you can latch it immediately after a trip it tripped almost certainly because of a fault and if so you better investigate the cause. Why? Because it is not a good thing to close a breaker back into a fault. Unlike a fuse you can reuse the breaker. In addition, if you question the calibration of a breaker it can be tested.

Fuses or breaker? Sometimes can be that you are a Chevy person think fords are a piece of crap or the other way around. You probably know someone like that. It may make no sense and maybe someone had a bad experience at one time which can occur with fuses vs. breakers. But them again it may simply be because of plain old stubbornness.

 

[augie47]

If you talk with a factory rep. each will give you a long list of why one device is superior.
From a practical standpoint, a lot of contractors here will install fusible disconnects as the unit requirements often don't match the panel breakers and it's easier to install the correct fuse than order/install a new breaker.

 

[jumper]

If you talk with a factory rep. each will give you a long list of why one device is superior.
From a practical standpoint, a lot of contractors here will install fusible disconnects as the unit requirements often don't match the panel breakers and it's easier to install the correct fuse than order/install a new breaker.

Most of the stuff I worked on was speced like this.

 

[jim dungar]

The HVAC rating has been a standard test for all UL Listed breakers for 15yr or more. In fact UL no longer requires a marking of 'HVAC rated' on breakers, although some inspectors still do.
Also, the HVAC rating has nothing to do with the trip characteristics (trip curve) of a breaker. It has been more than 40 yrs since ITE had a minature molded case circuit breaker specifically for motor loads.

 

[kwired]

Personal preference in most cases.

If available fault current is high you can often get higher rated breakers at a price. Fuses often have higher ratings to start with.

Fuses are one time thing. A forty year old fuse will likely still open when needed. A circuit breaker may be questionable if it will mechanically work when needed.

 

[jim dungar]

A forty year old fuse will likely still open when needed. A circuit breaker may be questionable if it will mechanically work when needed.

While a fuse element may open, a 40 year old switch may not. Evaluation of the pros and cons of fuse should also include the pros and cons of the equipment the fuse will be mounted into. For example, all fuses are 100% rated in open air, but they are only 80% rated when mounted into a fusible switch.

There is no one always correct answer.

 

[kwired]

While a fuse element may open, a 40 year old switch may not. Evaluation of the pros and cons of fuse should also include the pros and cons of the equipment the fuse will be mounted into. For example, all fuses are 100% rated in open air, but they are only 80% rated when mounted into a fusible switch.

There is no one always correct answer.

Absolutely, I always check safety switches after shutting them off. Have run into some that did not open a few times.

 

[ActionDave]

...... Have run into some that did not open a few times.

Or close; which has been a more frequent problelm in my experience.

 

[T.M.Haja Sahib]

From energy conservation point of view, I think in all breakers panel energy loss is less than in all fuses panel.But purchase cost of breakers panel is more.There may be a break even point for this......

 

[kwired]

Or close; which has been a more frequent problelm in my experience.

Or worse yet two of three close, or they don't fully engage leaving a high resistance connection.

 

[kwired]

From energy conservation point of view, I think in all breakers panel energy loss is less than in all fuses panel.But purchase cost of breakers panel is more.There may be a break even point for this......

Have you measured total heat from each - with identical loads connected?

I have no idea if one produces more heat than the other or not. But I will suggest that in the breaker panel all the heat producing components are closer together so the net heat may seem higher but all that matters from the energy conservation point of view is total watts lost.

 

[T.M.Haja Sahib]

A breaker panel is capable of 'instantaneous' trip, whereas a fuse panel is capable of 'inverse' trip only and so is not as fast.But in case of liquid lock in an air-conditioning compressor,a fast trip from supply might provide a better protection and in this way a breaker panel is better than a fuse panel.Just my opinion.

 

[T.M.Haja Sahib]

I have no idea if one produces more heat than the other or not.

Consider a breaker panel equipped with instantaneous trip only as it serves only motor loads of HVAC equipments.The panel does not have thermal elements in this case.

 

[kwired]

A breaker panel is capable of 'instantaneous' trip, whereas a fuse panel is capable of 'inverse' trip only and so is not as fast.But in case of liquid lock in an air-conditioning compressor,a fast trip from supply might provide a better protection and in this way a breaker panel is better than a fuse panel.Just my opinion.

There are time delay and non time delay fuses. They don't have to develop more or less heat than a comparable circuit breaker. If the device develops 1 watt of heat that heat will be first absorbed by any mass of conductive component connected to it. The more more mass there is the less heat will be given up as quickly to the air around it, and the air will be cooler - same heat is still given up. To truly know which is more energy efficient you can't just measure temperature you need to know how many actual watts are lost.

 

[T.M.Haja Sahib]

There are time delay and non time delay fuses.

I do not believe a non time delay fuse is a match for an instantaneous trip.

 

[kwired]

I do not believe a non time delay fuse is a match for an instantaneous trip.

Time delay fuses and inverse time breakers do not have the same trip curve either. We are talking about the heat given up during normal operation. Both will give up heat, they do not have to give up same amount of heat. A change of trip characteristics should change the rate that heat is given up.

 

[jim dungar]

Consider a breaker panel equipped with instantaneous trip only as it serves only motor loads of HVAC equipments.The panel does not have thermal elements in this case.

Breakers without thermal units are not used in anything except custom industrial panels. All of the UL 489 listed minature molded case breakers used in panelboards will have thermal elements.

 

[iwire]

Consider a breaker panel equipped with instantaneous trip only as it serves only motor loads of HVAC equipments.

That would be a violation 99% of the time.

 

[T.M.Haja Sahib]

I do not believe a non time delay fuse is a match for an instantaneous trip.

A current limiting fuse is,above a certain value of fault current:it operates faster than an ordinary breaker with an instantaneous trip.In this sense,the recommendation of the manufacturer of HVAC to use panel with current limiting fuses is justified,because in case of short at the HVAC motor terminals,the current limiting fuse offers better protection against contacts welding of the motor contactor.